716 
as in the water bath, which caused a 
fusion of the principal constituents and 
ferments in such a manner that the 
power of the ferments was destroyed. 
The investigations of scientists, partic- 
ularly of Pasteur, have shown that it is 
not the oxygen of the air which causes 
fermentation and putrefaction, but bac- 
teria and other microscopic organisms. 
Appert’s theory as to the cause of the 
spoiling of food was incorrect, but his 
method of preserving it by sealing and 
cooking was correct, and the world owes 
him a debt of gratitude. 
In their investigations scientists have 
found that if food is perfectly sterilized 
and the opening of the jar or bottle 
plugged with sterilized cotton, food will 
not ferment, for the bacteria and yeasts 
to which such changes are due cannot 
pass through the cotton. This method 
cannot be conveniently followed with 
large jars. 
Bacteria and yeasts exist in the air, in 
the soil, and on all vegetable and animal 
substances, and even in the living body, 
but although of such universal occur- 
rence, the true Knowledge of their nature 
and economic importance has only been 
gained during the last 40 years. 
There are a great many kinds of these 
micro-organisms. Some do great harm, 
but it is thought that the greater part of 
them are beneficial rather than injurious. 
Bacteria are one-celled and so small 
they can only be seen by aid of a micro- 
scope. The process of reproduction is 
simple and rapid. The bacterium becomes 
constricted, divides, and finally there are 
two cells instead of one. Under favorable 
conditions each cell divides, and so rapid 
is the work that it has been estimated 
that one bacterium may give rise, within 
24 hours to 17,000,000 of similar organ- 
isms. The favorable conditions for growth 
are moisture, warmth and proper food. 
Yeasts, which are also one-celled organ- 
isms, grow less rapidly. A bud develops, 
breaks off, and forms a new yeast plant. 
Some yeasts and some kinds of bacteria 
produces spores. Spores, like the dried 
seeds of plants, may retain their vitality 
ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 
for a long time, even when exposed to 
conditions which kill the parent organ- 
ism. 
Yeasts and nearly all bacteria require 
oxygen, but there are species of the latter 
that seem to grow equally well without 
it, so that the exclusion of air, which, of 
course, contains oxygen, is not always a 
protection, if one of the anaerobic bac- 
teria, as the kinds are called which do 
not require oxygen, is sealed in the can, 
Spoiling of food is caused by the de- 
velopment of bacteria or yeasts. 
Certain chemical changes are produced 
as shown by gases, odors and flavors. 
Bacteria grow luxuriantly in foods con- 
taining a good deal of nitrogenous mate- 
rial, if warmth and moisture are present. 
Among foods rich in nitrogenous sub- 
stances are all kinds of meat, fish, eggs, 
peas, beans, lentils, milk, ete. These 
foods are difficult to preserve on account 
of the omnipresent bacteria. This is seen 
in warm, muggy weather, when fresh 
meat, fish, soups, milk, etc., spoil quickly. 
Bacteria do not develop in substances 
containing a large percentage of sugar, 
but they grow rapidly in a suitable wet 
substance which contains a small per- 
centage of sugar. Yeasts grow very read- 
ily in dilute solutions containing sugars 
in addition to some nitrogenous and min- 
eral matters. Fruits are usually slightly 
acid and in general do not support bac- 
terial growth, and so it comes about that 
canned fruits are more commonly fer- 
mented by yeasts than by bacteria. 
Some vegetable foods have so much 
acid and so little nitrogenous substance 
that very few bacteria or yeasts attack 
them. Lemons, cranberries and rhubarb 
belong to this class. 
Temperature is an important factor in 
the growth of bacteria and yeasts. There 
are many kinds of these organisms, and 
each kind grows best at a certain temper- 
ature, some at a very low one and others 
al one as high as 125 degrees Fahren- 
heit, or more. However, most kinds of 
bacteria are destroyed if exposed for 10 
or 15 minutes to the temperature of boil- 
ing water (212 degrees Fahrenheit); but, 
if the bacteria are spore producers, cook- 
